1. Field of the Invention
This invention relates to a wireless data transfer method and system and, in particular, to a communication system, such as an electronic mail system, which carries out sending/receiving digital data between a plurality of terminals through a wireless transmission network in a network computer system.
2. Description of the Related Art
A wide variety of communication systems have been proposed to send/receive digital data between a plurality of wireless terminals included in a wireless computer network which is controlled by a computer network.
Among others, one type of mail sending/receiving system has widely prevailed. In this connection, such mail sending/receiving systems will be described with reference to FIGS. 1 and 2. FIG. 1 schematically shows an example of a conventional mail sending/receiving system. FIG. 2 shows a procedure based on a protocol used for sending/receiving a mail or mail data in each conventional mail sending/receiving system.
At first, description will be directed to a first one of the conventional mail sending/receiving systems.
It is assumed that a mail (mail data) includes a mail header and a mail body. When a wireless terminal is used for an electronic mail system in a LAN (local area network) through a wireless communication network (for example, a mobile radio telephone network) a wireless terminal A 201 sends both a mail header and a mail body addressed to a wireless terminal B 203 to a mail server 202 (S402). Next, the mail server 202 stores the mail header and the mail body which are received (S403). The wireless terminal B 203 can connect to the mail server 202 in anytime, and when the wireless terminal B 203 determines that the mail header and/or the mail body addressed to it exist in the mail server 202 (S404, S405), it receives the mail header and/or the mail body from the mail server 202 (S406, S407). A wireless electronic mail receiving system which has been disclosed in Japanese Laid Open Publication No. HO8-139747 is similar in structure to the first conventional system.
It is a problem that, in a mail sending/receiving system as the first conventional system, a recipient of a mail cannot know contents of the mail until a wireless terminal B completes the reception of a mail header and a mail body of the mail. In other words, when a recipient wants to know contents of a mail, a wireless terminal B must receive both of a mail header and a mail body from the mail server. Even if the recipient does not need the mail or does not want to receive the mail, the mail header and the mail body of the mail are transferred to the wireless terminal B. Consequently, during the transfer, a wireless transmission network is used as transmission network and the recipient is to be charged according to the duration of use of the transmission network.
Such a problem becomes serious when a size of the mail header for each mail becomes small (for example, the size is about 10 through 100 bytes) and a size of the mail body for each mail becomes large. For example, a transmission time of about 14 minutes is needed for the transfer when the size of mail body is as long as 1 megabytes if transmission is carried out from a standard communication device which has a transmission rate of 9,600 bit per second (1 byte=8 bits). The above transmission time is measured on the assumption that disconnection neither takes place due to interference during the transmission time executed by the recipient nor any retry operation is repeated.
When disconnection occurs during reception of the mail body, the reception operation must be repeated by the recipient. A probability of occurrence of radio-frequency interference, which is one of the reasons for disconnection, is generally kept constant over the whole transfer time. However, during successive data transmission, as the data size becomes large, the probability of occurrence of the radio-frequency interference becomes high during transmission. As a result, the recipient often wastes money when the network is used for providing service of the network connection serve provider during a transmission time.
In a system, such as the first conventional system, when a sender sends a great deal of mail information to a lot of recipients in the form of an advertising direct mail, some or most of the recipients might neither need such mail information nor want to see the mail. This brings not only about a serious economical loss but also wastes a network resource.
On the contrary, if a mail body of about 1,000 through 5,000 bytes is received, a recipient does not suffer an economical loss since a cost for the reception of such a short mail body is as small as a cost for the reception of the mail header.
It is assumed that an account operation is carried out at every one of six seconds while a mail header and a mail body of 5,000 bytes are received for one second and five seconds, respectively. Under the circumstances, if a recipient receives only the mail header, the recipient pays for using the network for six seconds although he or she uses the network for one second. On the other hand, when the recipient receives both the mail header and the mail body, the recipient also pays for charges for using the network for six seconds. In the later case, the recipient does not pay for extra money, since it takes just six seconds to receive the mail header and the mail body.
Next, a second conventional system will be described with respect to the Figures of the first conventional system.
The second conventional system functions in the same way as the mail sending/receiving method shown in FIG. 1. In the second conventional system, a wireless terminal A 201 sends a mail including a mail header and a mail body to a mail server 202. Next, when a wireless terminal B 203 receives the mail, the wireless terminal B 203 receives only the mail header. If a user which received the mail header determines that the mail is necessary, the wireless terminal B 203 receives the remaining mail body.
According to the second conventional system, when the wireless terminal B 203 need not receive the mail body, it can instruct the mail server 202 to delete the mail body in the mail server 202. Therefore, the second conventional system can reduce traffic in a transmission network between the mail server 202 and the wireless terminal B 203 by eliminating transferring unnecessary mail data between them. This is one of the merits in the second conventional system, as compared to the first conventional system. An electronic mail delivery system which has been disclosed in Japanese Laid-Open Publication No. HO1-236541 is similar to the second conventional system.
Here, for the sake of clarity, it is assumed that the wireless terminal A 201 sends a mail and the wireless terminal B 203 receives the mail in the above description. However, it is readily understood that the wireless terminal B 203 also can send a mail to the wireless terminal A 201 by exchanging functions of the above two terminals.
The mail sending/receiving system according to the second conventional system can overcome the problem in the first conventional system to some extent.
In the system, the wireless terminal B at first receives only a mail header on reception of the mail information from the mail server. Then, a recipient can determine whether or not a mail body is necessary for the recipient by referring to a size of the mail body, a title, and so on included in the mail header. Therefore, the recipient can select only necessary mail information to be received and may pay a reduced fee as compared to the first conventional system.
However, the second conventional system can not favorably cope with sending a large number of mails. Specifically, when a wireless terminal A simultaneously sends a plurality of destinations, such as over 1,000 terminals, mail information including a plurality of mails each of which includes a mail header and a mail body similar to one another all storage regions in a mail server is occupied with the mail headers and the mail bodies because all of the mail headers and the mail bodies which are produced in the wireless terminal A are once sent to the mail server.
This situation may occur when a large amount of commercial direct mails are produced and are transmitted by automatically replacing only destinations in the mail header and recipient names in the mail header. All the wireless terminals each of which corresponds to a destination of a mail do not immediately receive or delete the mail headers. In other words, the wireless terminals can individually receive or delete them in each timing assigned to each of the corresponding recipients.
When a large amount of mail information is simultaneously sent to the mail server, as mentioned before, all of the mail information or a part of the mail has been received in the mail server and kept in the mail server for a long time. As a result, a storage resource are wasted in the mail server.
Furthermore, the second conventional system has another disadvantage. Herein, let the wireless terminal A send a large amount of mail headers and mail bodies to a plurality of destinations, such as over 1,000 terminals in the above-mentioned case. Under the circumstances, all of the mail headers and mail bodies are stored in the mail server through the wireless transmission network between the wireless terminal A and the mail server. Furthermore, when the wireless terminals B each of which corresponds to one of the destinations receive the corresponding mail (including a mail header and a mail body), the mail is sent through a wireless transfer network between the mail server and receiving wireless terminal as similar to when it is stored in the mail server.
Therefore, providing that a mail header and a mail body which are sent by the wireless terminal A are received by the wireless terminal B, in the mail sending/receiving system according to the first and the second conventional system, the mail header and the mail body occupy the wireless transmission network twice on transmission and reception of the mail.
For example, when the mail body is less than or equal to 5,000 bytes in size, no problem takes place in connection with occupation of the memory. However, when the mail body becomes large in size, the memory resource is largely occupied in the whole mail system.
In addition, a wireless terminal device is also disclosed in Japanese Laid-Open Publication No. II07-183824. In the wireless terminal device, wireless terminals (A and B) are turned on only when the wireless terminals automatically communicate with each other, and turned off when they complete their communication. This device is useful for saving power in batteries included in the wireless terminals.
At any rate, this device still wastes power in the batteries because each wireless terminal is activated and connected to the mail server for communication, even if no information for simultaneous communication is present in both the mail server and each wireless terminal.
It is therefore an object of the invention to provide a wireless terminal device which is capable of solving the above-mentioned problems.
It is a specific object of the invention to provide a method of reducing a fee which results from reception of unnecessary mail information.
It is another object of the invention to provide a method of reducing both resources of a wireless transmission network occupied in the whole system and storage resources occupied in a center-machine (server).
It is still another object of the invention to provide a method of suspending communication automatically according to degradation of quality of a wireless network or requests for the network by a user, and restarting the communication automatically so as to achieve data transmission without fail.
It is still another object of the invention to provide a method suspending communication automatically and for saving a resource of battery power of a wireless terminal.
According to the invention, in a wireless data transfer method for sending/receiving digital data between terminals via a center-machine by using a wireless transmission network, the method comprising the steps of sending a mail header including attribute information of the digital data from a source terminal to the center-machine and receiving the digital data by a destination terminal from the source terminal when the digital data is determined to be necessary by referring to the mail header in the center-machine is provided.
Furthermore, the attribute information of the digital data includes an ID identifying the source terminal, a size of the digital data, a title of the digital data, and an ID identifying the digital data.